Fluid drilling head nozzle design

ABSTRACT

A fluid cutting head of the type having a plurality of nozzles in a rotatable nozzle assembly for cutting a bore hole in rock. The cutting head has nozzles arranged to be supplied with high pressure drilling fluid, forming jets positioned to cut adjacent rock. The nozzles include one or more generally axially facing pilot nozzles, and one or more generally radially facing reaming nozzles. At least the pilot nozzles include a non-tapering outlet section such that the jet issuing therefrom is of substantially constant cross-section in a zone immediately adjacent the outlet section. The pilot nozzles are located in a leading part of the rotatable nozzle assembly, and have a minimized diameter. The reaming nozzles are located in the following part of the rotatable nozzle assembly. The following part of the rotatable nozzle assembly is formed in a step-wise fashion to keep the reaming nozzles close to the rock face.

This invention relates to the design of the nozzles and rotatable nozzleassembly for a fluid drilling head of the type generally described inour earlier international patent application PCT/AU02/01550(international publication No. WO 03/042491 A1), the content of which isincorporated herein by way of cross reference.

BACKGROUND OF THE INVENTION

In previously known forms of fluid drilling heads, it has been common touse a type of nozzle known as a “horn nozzle” having a diverging outletportion designed to produce a powerful cavitation cloud for the cuttingor breaking of rock in the drilling operation. Such a device is shown inFIG. 2 of this specification.

Further research by the applicants has shown that while the cavitationcloud generated by horn nozzles of this type is indeed powerful, it isgenerated at a position remote from the nozzle outlet. The zone betweenthe cavitation cloud and the nozzle outlet is a “dead zone” which is noteffective in cutting rock adjacent to the nozzle outlet. Accordingly,placement of such nozzles to generate smooth and self-advancing geometryis very difficult due to the dead zone immediately in front of the pilotjets at the leading edge of the fluid cutting head, and effective designof the fluid cutting head is also difficult due to the physical size ofthe horn nozzles. Prior art devices of the type shown in FIG. 2 need tobe fed slowly into the bore hole to ensure the rock being cut staysremote from the front of the head. If the tool gets too close to therock, the rock would be in the dead zone and a “stall” would result.

SUMMARY OF THE INVENTION

The present invention therefore provides a fluid cutting head of thetype having a plurality of nozzles in a rotatable nozzle assembly forcutting a bore hole in rock, said nozzles being arranged to be suppliedwith high pressure drilling fluid, forming jets positioned to cutadjacent rock, said nozzles including one or more generally axiallyfacing pilot nozzles and one or more generally radially facing reamingnozzles, at least the pilot nozzles being characterised by anon-tapering outlet section such that the jet issuing therefrom is ofsubstantially constant cross-section in a zone immediately adjacent theoutlet section.

Preferably, the reaming nozzles are also characterised by a non-taperingoutlet section such that the jet issuing therefrom is of substantiallyconstantly cross-section in a zone immediately adjacent the outletsection.

Preferably, the leading part of the rotatable nozzle assemblyincorporating the pilot nozzles is of significantly lesser diameter thanthe following part of the rotatable nozzle assembly incorporating thereaming nozzles.

Preferably, the following part of the rotatable nozzle assembly isformed in a stepwise fashion of steps of progressively increasingdiameters, there being one reaming nozzle located in each step such thatthe jet issuing from each reaming nozzle is located close to theadjacent bore hole surface.

BRIEF DESCRIPTION OF THE DRAWINGS

Notwithstanding any other forms that may fall within its scope, onepreferred form of the invention will now be described by way of exampleonly with reference to the accompanying drawings, in which:

FIG. 1 is side view of a fluid drilling head according to the invention;

FIG. 2 is a diagrammatic representation of a prior art fluid drillinghead showing the formation of cavitation clouds remote from the nozzleoutlets;

FIG. 3 is a right hand perspective view of the rotatable nozzle assemblyof a fluid drilling head according to the invention;

FIG. 4 is a left hand perspective view of the rotatable nozzle assemblyof a fluid drilling head according to the invention;

FIG. 5 is an end view of the rotatable nozzle assembly shown in FIGS. 3and 4;

FIG. 6 is a side view of the rotatable nozzle assembly shown in FIGS. 3and 4, and

FIG. 7 is a cross-sectional view through a nozzle of the type used inthe fluid drilling head according to the invention.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS OF THE INVENTION

In the preferred form of the invention, a fluid drilling head 8typically has a rotatable nozzle assembly 9 and may incorporate otherfeatures such as a gauging ring 10 mounted at the leading end of a drillhead body 11.

The more detailed configuration of the rotable nozzle assembly 9 will bedescribed below with reference to FIGS. 3 to 7, which demonstrate howthe nozzle design and placement can be optimised to overcome theproblems of a typical prior art fluid drilling head of the type shown at12 in FIG. 2.

In the typical prior art fluid drilling heads, the rotatable nozzleassembly 13 is provided with pilot nozzles 14 and reaming nozzles 15which are typically of a “horn nozzle” design having a diverging outletportion. Nozzles of this type generate powerful cavitation clouds showndiagrammatically at 16 which are effective in cutting and breaking uprock. It has been found through careful laboratory testing that whilethe cavitation clouds 16 generated by the nozzles 14 and 15 are indeedpowerful, they are remote from the nozzle outlets as clearly shown inFIG. 2 resulting in a “dead zone” 17 between the cavitation cloud 16 andthe nozzle outlets. Because of the dead zone, prior art tools of thisnature need to be fed slowly into the hole to ensure that the rock beingcut stays remote from the front surface 18 of the head. Once the frontsurface 18 advances too quickly into the rock face, the cavitation cloud16 is no longer effective and the jet issues against the rock face inthe dead zone 17.

The present invention overcomes this deficit by providing nozzles of thetype shown in FIG. 7 where the nozzle 18 is typically inserted into ahole 19 formed in the rotatable nozzle assembly 20 and secured in placeby a threaded engagement 21.

The nozzle is typically formed to sit in a counter bore 22 such that thetop of the nozzle thread 23 sits flush with the base of the counterbore.

While the inlet portion 24 of each nozzle is typically tapered inwardlyto increase the velocity of the high pressure water pumped through thenozzle, the outlet section 25 is formed of non-tapering section as isclearly seen in FIG. 7 such that the jet issuing therefrom is ofsubstantially constant cross-section in the zone immediately adjacentthe outlet section.

It has been found that the use of nozzles formed to this configurationresults in a jet which is effective at cutting or breaking rockimmediately adjacent the outlet from the nozzle, so avoiding the deadzone 17 typically found in the prior art nozzle configurations.

In order to maximise the rock cutting effect of nozzles of this type, ithas also been found most effective to form the rotatable nozzle assemblyin steps such that the leading part 26 incorporating the pilot nozzlesforming jet 1 and jet 2 is of significantly lesser diameter than thefollowing part 27 of the rotatable nozzle assembly incorporating thereaming nozzles.

The reaming nozzles 3, 4, 5, and 6 are typically located to providereaming jers as shown in FIGS. 3 and 4 and are located at 29, 30, 31 and32 respectively as can be clearly seen in FIG. 6.

In this manner, the following part 27 of the rotatable nozzle assembly 9is formed in a stepwise fashion of progressively increasing diameters,there being one reaming nozzle located in each step such that the jetissuing from each reaming nozzle is located close to the adjacent borehole surface.

This has been found to be most effective in maximising the operation ofeach reaming jet, allowing the reaming jets to issue from their nozzlesclose to the surface of the bore hole to be reamed and enlarged untilthe final bore hole diameter is achieved. Ultimately, the bore holediameter is controlled by the gauging ring 10.

This effect is optimised by reducing the diameter of the leading part 26as much as physically possible so that the pilot jet rock cuttingfunction is reduced compared with the progressive enlargement of thebore hole diameter from the reaming jets in the following stepped parts27.

Combined with the use of nozzles of the type described above, thisallows the reaming jets to operate close to the rock face and increasethe diameter of the bore in a step-wise manner. There rearward facingorientation of the reaming jets also allows much more efficient rockbreaking at this close proximity.

Laboratory testing has shown that the zone within about 5 mm of theoutlet from each reaming jet is very destructive, and much more so thanthe remote cavitation cloud of the horn nozzles used in prior artdevices.

The actual diameters of the nozzle outlets are selected depending on thenature of the rock to be cut, as is the pressure of the water suppliedto the nozzles through the fluid drilling head. Testing has shown thatdrilling is effective at pressures of 48 MPa to 73 MPa. 48 MPa is betterin bright coals, and 73 MPa is better in claystone bands and sandstone.

Nozzle diameters vary depending on the material and nozzle location. Thefront pilot nozzles need be no greater than 0.7 mm to 1.0 mm indiameter. It is best to minimise these sizes to improve net tool forwardthrust, and a small change makes a big difference as they pointvirtually straight ahead. The reamers work well in the range between 0.5mm and 1.3 mm, again depending on the coal conditions. The 310 m holewas drilled with 0.8 straight ahead, 0.9 forward angled, and 1.1 in thethree reamers in this head. This, however, produced a penetration rateof around 1 m/min.

In this manner, a rotatable nozzle assembly for a fluid drilling headcan be provided which allows faster drilling rates than has previouslybeen achieved with prior art drilling heads and further allows moreaccurate control of the bore hole size, and the effective location ofthe reaming nozzles.

1. A fluid cutting head of the type having a plurality of nozzles in arotatable nozzle assembly for hydraulically cutting a bore hole in rock,said nozzles being arranged to be supplied with high pressure drillingfluid, forming jets positioned to cut adjacent rock, said nozzlesincluding one or more generally axially facing pilot nozzles and one ormore generally radially facing reaming nozzles, at least the pilotnozzles including a non-tapering outlet section such that the jetissuing therefrom is of substantially constant cross-section in a zoneimmediately adjacent the outlet section, and wherein the leading part ofthe rotatable nozzle assembly incorporating the pilot nozzles is ofsignificantly lesser diameter than the following part of the rotatablenozzle assembly incorporating the reaming nozzles.
 2. A fluid cuttinghead as claimed in claim 1, wherein the reaming nozzles comprise anon-tapering outlet section such that the jet issuing therefrom is ofsubstantially constantly cross-section in a zone immediately adjacentthe outlet section.
 3. A fluid cutting head as claimed in claim 2wherein the reaming nozzles are oriented such that the jets issuingtherefrom are angled rearwardly relative to the direction of travel ofthe cutting head.
 4. A fluid cutting head as claimed in claim 1 whereinthe following part of the rotatable nozzle assembly is formed in astepwise fashion of steps of progressively increasing diameters, therebeing at least one reaming nozzle located in each step such that the jetissuing from each reaming nozzle is located close to the adjacent borehole surface.
 5. A fluid cutting head as claimed in claim 1 wherein oneor more of the nozzles have an inlet portion of inwardly taperingsection upstream of the non-tapering outlet section.
 6. A fluid cuttinghead as claimed in claim 1 wherein the pilot nozzles have an internaldiameter less than 1.0 mm.
 7. A fluid cutting head as claimed in claim 1wherein the reaming nozzles have an internal diameter less than 1.3 mm.8. A fluid cutting head as claimed in claim 7 wherein the reamingnozzles have an internal diameter between 0.5 mm and 1.3 mm. 9.(canceled)
 10. A fluid cutting head as claimed in claim 2 wherein thefollowing part of the rotatable nozzle assembly is formed in a stepwisefashion of steps of progressively increasing diameters, there being atleast one reaming nozzle located in each step such that the jet issuingfrom each reaming nozzle is located close to the adjacent bore holesurface.
 11. A fluid cutting head as claimed in claim 3 wherein thefollowing part of the rotatable nozzle assembly is formed in a stepwisefashion of steps of progressively increasing diameters, there being atleast one reaming nozzle located in each step such that the jet issuingfrom each reaming nozzle is located close to the adjacent bore holesurface.
 12. A fluid cutting head as claimed in claim 4 wherein thefollowing part of the rotatable nozzle assembly is formed in a stepwisefashion of steps of progressively increasing diameters, there being atleast one reaming nozzle located in each step such that the jet issuingfrom each reaming nozzle is located close to the adjacent bore holesurface.
 13. A fluid cutting head as claimed in claim 2 wherein one ormore of the nozzles have an inlet portion of inwardly tapering sectionupstream of the non-tapering outlet section.
 14. A fluid cutting head asclaimed in claim 3 wherein one or more of the nozzles have an inletportion of inwardly tapering section upstream of the non-tapering outletsection.
 15. A fluid cutting head as claimed in claim 4 wherein one ormore of the nozzles have an inlet portion of inwardly tapering sectionupstream of the non-tapering outlet section.
 16. A fluid cutting head asclaimed in claim 10 wherein one or more of the nozzles have an inletportion of inwardly tapering section upstream of the non-tapering outletsection.
 17. A fluid cutting head as claimed in claim 11 wherein one ormore of the nozzles have an inlet portion of inwardly tapering sectionupstream of the non-tapering outlet section.
 18. A fluid cutting head asclaimed in claim 12 wherein one or more of the nozzles have an inletportion of inwardly tapering section upstream of the non-tapering outletsection.
 19. A fluid cutting head as claimed in claim 2 wherein thepilot nozzles have an internal diameter less than 1.0 mm.
 20. A fluidcutting head as claimed in claim 3 wherein the pilot nozzles have aninternal diameter less than 1.0 mm.
 21. A fluid cutting head as claimedin claim 4 wherein the pilot nozzles have an internal diameter less than1.0 mm.